My friend was looking to buy a 2004 gto, very much modded. Not sure what was in it. But The car would crank up, and then immediately shut down. If you revved the engine up it would stay but if you let your foot off the gas it would immediately shut down. it Wasn't because of the Cam. I was wondering if anyone had any answers?

 

A vacume leak would cause it.... you said very modded, how do you know its not the cam? Could be timing too, but I would look for vacume leaks first.

 

It wasnt the lope, it literally would just turn over and shut off.

 

Check the fuel pressure/pump/filter,

To be honest, I am working on a '96 VW VR6 with the same symptoms and issues that you describe. And that is what we have found out. Weak pressure due to worn out fuel pump cause by clogged fuel filter. Shame and will cost a fortune but must be done..... Right??

 

Don't buy modded cars that run bad, you don't know where they have been, or who molested them. An you will wind up spending much time and money to get them working right.